介绍

在 iOS 17 之前，UIView Animation 已经提供了弹簧动画的 API。

open class func animate(withDuration duration: TimeInterval,
                        delay: TimeInterval,
                        usingSpringWithDamping dampingRatio: CGFloat,
                        initialSpringVelocity velocity: CGFloat,
                        options: UIView.AnimationOptions = [],
                        animations: @escaping () -> Void,
                        completion: ((Bool) -> Void)? = nil)

iOS 17 为弹簧动画增加新的 API。

@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
@MainActor public class func animate(springDuration duration: TimeInterval = 0.5,
                                     bounce: CGFloat = 0.0,
                                     initialSpringVelocity: CGFloat = 0.0,
                                     delay: TimeInterval = 0.0,
                                     options: UIView.AnimationOptions = [],
                                     animations: () -> Void,
                                     completion: ((Bool) -> Void)? = nil)

参数含义

springDuration：动画持续的时间。
bounce：弹性系数，取值范围 0 ～ 1，数值越大弹性效果越明显。
initialSpringVelocity：初始速度，数值越大初始速度越快。
delay：动画延迟执行的时间。
options：动画的执行效果，可以组合使用。
animations：能够产生动画的具体操作。
completion：动画执行完毕后的操作。

案例

import UIKit

class ViewController: UIViewController {
    lazy var redView: UIView = {
        let view = UIView(frame: CGRect(x: 0, y: 50, width: 100, height: 100))
        view.backgroundColor = .red
        return view
    }()
    lazy var greenView: UIView = {
        let view = UIView(frame: CGRect(x: 120, y: 50, width: 100, height: 100))
        view.backgroundColor = .green
        return view
    }()
    lazy var blueView: UIView = {
        let view = UIView(frame: CGRect(x: 240, y: 50, width: 100, height: 100))
        view.backgroundColor = .blue
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(blueView)
        view.addSubview(greenView)
        view.addSubview(redView)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        animate()
    }
}

extension ViewController {
    // MARK: UIView动画
    func animate() {
        // 3个不同参数的弹簧动画对比
        UIView.animate(springDuration: 1.5, bounce: 0) {
            self.redView.center.y = 300
        }
        UIView.animate(springDuration: 1.5, bounce: 0.5, initialSpringVelocity: 5) {
            self.greenView.center.y = 300
        }
        UIView.animate(springDuration: 1.5,
                       bounce: 0.9,
                       initialSpringVelocity: 10,
                       delay: 0,
                       options: .curveLinear,
                       animations: {
                           self.blueView.center.y = 300
                       }, completion: nil)
    }
}